1. Field of the Invention
This invention relates to a homogeneous slurry-type blasting composition, and to a method and system for making such.
2. Prior Art Relating to the Invention
Aqueous and oil-based inorganic nitrate slurry explosives are extensively used in strip mining of coal and other construction uses. These slurry-type explosives generally contain a major amount of an inorganic nitrate and a fuel together with water or oil and a thickening or gelatinizing agent. The most common way of making slurry-type explosive compositions has generally involved employing an aqueous solution of ammonium nitrate or alkali or alkaline earth metal nitrates to which the other components are added. Finely divided aluminum flakes are commonly used in such compositions; however, "dusting" of this particulate material during manufacture of blasting compositions presents an extreme hazard. It is also difficult to obtain a homogeneous mix of the metal nitrate and metal particles without segregation. If the components are not uniformly mixed, the explosive composition either does not detonate or performs unsatisfactorily.
It has remained a problem to develop a slurry-type explosive composition which can be manufactured quickly, without the need for special equipment, at reasonable cost, and with safety.
The following U.S. patents disclose slurry-type blasting compositions and methods of making them; however, none of them employ a method or composition as described and claimed herein.
U.S. Pat. No. 3,294,601 discloses a slurry-type blasting composition of ammonium nitrate as an oxidizer, hexamethylenetetramine as a fuel, water, and a thickening or gelling agent. No particulate metal as a fuel is employed. The blasting composition is formed by mixing the ammonium nitrate, gelling agent together in a steam-jacketed vessel to melt them and slowly adding to the dry, hot melted mixture hexamethylenetetramine dissolved in boiling water, the mixture being blended until a cohesive mass is formed.
U.S. Pat. No. 3,765,967 discloses a slurry explosive prepared by dissolving an inorganic metal perchlorate in water together with a thickener and particulate pentaerythritol tetranitrate and adding finely divided aluminum to the aqueous slurry.
U.S. Pat. No. 5,985,593 discloses a method of making a slurry explosive by solubilizing nitromethane in an aqueous gel of sodium perchlorate which includes a solubilizing agent for the nitromethane, such as ethylene glycol.
U.S. Pat. No. 3,787,254 discloses a water-base slurry composition made by distributing a liquid hydrocarbon fuel in an emulsion-like form of a mixture of ammonium nitrate and calcium nitrate, and then adding a thickening or gelling agent. Aluminum metal is added as a secondary fuel for certain of the compositions.
U.S. Pat. No. 3,886,010 discloses a water-base slurry composition made by incorporating a small amount of a thickener to an aqueous oxidizing solution of amonium nitrate and thereafter adding a dry mix of a particulate solid fuel, such as finely divided aluminum, to the solution by stirring and mixing, the dry mix including a supplemental thickening agent and a cross-linking agent.
U.S. Pat. No. 3,378,416 discloses an explosive slurry made by melting together the liquefiable component of the composition, i.e., ammonium nitrate and sodium nitrate, and then mixing in a dough-type mixer the mixture of the metal nitrates and a carbonaceous fuel, such as starch or woodmeal; a particulate metal, such as aluminum powder or flake; water; and a thickening agent, if needed. It is essential to melt the liquefiable ingredients first and then add the fuel and other ingredients to avoid spontaneous ignition thereof.
U.S. Pat. No. 3,235,425 discloses a sequence of steps for mixing a slurry-type blasting composition by mixing together a dry mixture of ammonium nitrate and a gelling agent, then adding the resulting dry mix to water, and thereafter mixing in a smokeless powder.
None of the patents disclose a sequence of mixing steps to avoid dusting of particulate metal such as aluminum used as a fuel in the production of blasting compositions nor a method which avoids desensitizing the composition during manufacture.